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    Re: Lunar eclipses and other things
    From: Alexandre Eremenko
    Date: 2004 Oct 27, 13:08 -0500

    Dear Herbert,
    Thank you very much for your careful analysis of my message,
    and especially for your corrections to my statements.
    I reply to some of your comments on my message,
    but let me make a general disclaimer first.
    I am not a professional historian, and the purpose
    of that message was only to bring some subjects
    to this list. The statements I made reflect only
    my general impression from what I read on the subject
    over the years, and I am not ready to confirm all
    of them with precise references. And of course I am
    thankful to any corrections to these statements.
    
    On Wed, 27 Oct 2004, Herbert Prinz wrote:
    
    > Why was any lunar theory
    > (whether that of Hipparchus or anybody else) required to interpret the
    > dates?
    
    I have to dig the literature for more precise info.
    But Lunar eclipses (and other historical records of astronomical
    observations)
    are frequently used by historians to establish
    the real dates of the past events.
    
    > We know nothing about the Chaldeans ???
    
    Replace it by: "I don't know anything about Chaldeans".
    I mean I don't know the names of those Chaldeans and where
    and when and how they made their observations. (Somewhere
    in the modern Iraq territory, I suppose?)
    Do we have their own records or only mentioning in secondary
    sources? I would be grateful if you provide more precise
    info about them, or references.
    
    > To be sure, it remained the only ASTRONOMICAL method,
    
    Agree.
    
    > people collected their knowledge of longitudinal distances
    > through travelling.
    
    My impression was that this was much less precise.
    For example, in Erathosphenes measurement of the Earth
    radius, the main technical problem was how to measure
    the distance on the land, not the angle in the sky.
    And it is the error in this land distance that limited
    the presision of his method. And how indeed would you measure
    a distance when traveling? I mean in those ancient times.
    In "days of the
    travel".
    And how do you insure that you travel on a straight line?
    
    > > This was the only method Columbus could use.
    > But in fact, he used dead reckoning. He tried to confirm it twice with
    > an eclipse.
    
    Of course. I meant the only ASTRONOMICAL method of
    determining LONGITUDE. Everyone knows Columbus was an
    "unsurpassed genius of dead reckoning").
    
    > He used one lunar eclipse mainly to frighten the poor Red
    > Indians.
    
    Really? I thought he was really very concerned about his longitude.
    
    > > due to the general collapse of knowledge and educcation,
    > > which came soon after
    > > Ptolemy and lasted for about 1500 years).
    > Let us not sweep eight centuries of Arab science under the rug ....
    
    Yes, of course. And Iran and Middle Asia, and maybe China and India.
    Of course I meant "the West", first of all.
    More precisely, the Roman Empire
    or whatever remained of it.
    But I add: even if we take into account ALL the world
    together, the period from Ptolemy to approx XVII century was
    a hudge decline (in science) in comparison  with the
    "First scientific revolution" which happened in Ellinistic World
    approx in 3-d century BC.
    
    I realize that this is not conventional point of view, and maybe
    a full scale discussion of this is out of the scope of this list, so
    I just give a reference to the author whose views on this
    subject I share:
    Lucio Russo, The Forgotten Revolution. How the science was
    born in 300 bc and why it had to be reborn", translated
    from Italian, Springer-Verlag (Berlin, NY, etc.) 2004.
    
    > Lunar eclipses never played any role in map making before Mayer. The
    > method was too crude.
    
    I doubt about both statements. But cannot refute the first
    at this moment; this would require a history research.
    About the second statement, I think we can easily
    decide by giving specific numbers.
    Unfortunately the sky is obscured today so I cannot observe
    the eclipse myself:-( But what do you think the precision of the
    method would be with observation tools of 1000-2000 years ago?
    My first prelininary guess would be:
    5 degrees in field conditions with an astrolabe,
    and from 30' to 1 degree in a reasonable observatory.
    
    > It was
    > thus Ptolemy's lunar theory that lasted - but only as far as longitude
    > is concerned - without a major modification until Brahe added the term
    > for variation.
    
    When I was talking of "Hipparchus lunar theory" I did not separate
    it from Ptolemy's. I simply don't know how do do it: Hipparchus original
    work did not survive, and it is known to us mainly through Ptolemy.
    Whether Ptolemy "improved Hipparchus theory" of "replaced it
    by his own improved theory" is just the question of wording from
    my point of view.
    
    > Kepler hit on the "annual equation" around the same time as Brahe.
    
    At the time when he was Brahe's assistant?
    
    > is not much, as you say, but in fact it is
    
    My statements should not be interpreted as trying to diminuish
    Kepler's achievements:-)
    
    Alex.
    
    
    

       
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